Techniques for printing a pattern or image comprised of a plurality of individual targets or pixels arranged in a grid involve the use of printheads, often referred to in the art as pens. The printheads typically are moved along a scan axis in a forward scan direction, then after stopping, moved in a reverse scan direction opposite to the forward scan direction. In between at least some of the movements along the scan axis, the print medium is typically advanced in a media advance direction whose axis is substantially orthogonal to the scan axis. Printheads typically have a plurality of ink ejection elements, each of which controllably ejects ink through a corresponding nozzle on the surface of the printhead and onto the print medium. One characteristic of a printhead is its effective nozzle density, expressed for example in printhead nozzles per inch (pnpi), which can be greater than or equal to the required print density expressed in printed dots per inch (dpi).
The present invention therefore provides a method and apparatus for placing fluid droplets onto a surface in which at least one of a group of nozzles is substantially aligned with a first of parallel line segments on a surface moving in a first direction relative to said nozzles; at least one droplet is ejected from said first nozzle onto a target on said first segment; said group of nozzles is moved relative to said surface in a second direction having a component orthogonal to said first direction and another component parallel to said first direction to respectively align first and second nozzles in said group with a second segment and with said first segment; and droplets are ejected from said nozzles onto targets on said segments, the center to center spacing of said targets along said segments equaling one or a multiple of the center to center spacing of said nozzles orthogonal to said segments.